Process of preparing triazenes



latentecl Sept. 1950 2,521,095 PROCESS OF PREPARING TRIAZENES Henry H. Richmond, assignor to United New York, N.

Guelph, Ontario, Canada, States Rubber Company,

Y., a corporation of New Jersey No Drawing. Application October 18, 1947 Serial No. 780,745

11 Claims. (Cl. 260-140) This invention relates to a process of preparing symmetrical triazenes especially xenyltriazenes. Symmetrical triazenes, which have the general formula RN=N-Nl-I-R where the Rs are identical aryl groups, have heretofore been made by the condensation of aromatic amines with alkyl nitrites, especially amyl nitrites using ethanol, ether and ethyl acetate as solvents. However, the presence of ethanol in the reaction mixture decreases the yield. The use of ether as a solvent is impractical because of the hazard and ethyl acetate is too expensive. Furthermore the triazenes are soluble in the solvents previously employed, making the isolation of the product more difiicult.

Triazenes are more usually prepared by the diazotization of the mineral acid salts of the arcmatic amines in aqueous solution followed by further condensation with additional amine in neutral or weakly acid media. However, this process cannot be used satisfactorily with amines whose mineral acid salts are either sparingly soluble in water or readily hydrolyzed by water. Examples of such amines are p-xenylamine and m-xenylamine.

The principal object of the present invention is to provide an improved method of making symmetrical triazenes. Another object is to provide an improved method of making symmetrical xenyltriazenes. Another object is to provide a meth- 0d of the foregoing type which gives very high yields of the desired product expeditiously and at low cost. Another object is to provide a method of the foregoing type which is particularly adapted to those aromatic amines whose mineral acid salts are sparingly soluble in water or are readily hydrolyzed by water so that diazotization is difiicult. Another object is to provide an improvement in the alkyl nitrite method of making triazenes whereby the storage and handling of an unstable and dangerous alkyl nitrite such as amyl nitrite is avoided. Numerous other objects will .more fully hereinafter appear.

I have discovered that symmetrical xenyltria- 'zenes may be prepared in an improved manner by reacting a zenylamine with an alkyl nitrite while the amine is dissolved in a normally liquid solvent selected from the group consisting of benzene,

homologs of benzene, mono-ring-halogenated benzene and mono-ring-halogenated homologs of benzene, whereby the triazene is precipitated and can subsequently be separated from the resulting reaction mixture in any convenient manner, typically by filtration.

The general procedure of my invention involves contacting the xenylamine with an alkyl nitrite in solution in an aromatic hydrocarbon solvent such as benzene, toluene or xylene or an aromatic halide solvent such as chlorobenzene. The xenyltriazene separates out as a mass of crystals of satisfactory purity. The xenyltriazene is but sparingly soluble in solvents of the class enumerated above while the amine is quite soluble in it, and in this way the triazene precipitates and is readily removed by filtration.

While the process of my invention is especially advantageous in the preparation of 1,3-bis(p xenyl) -triazene and' 'l,3bis(m-xenyl) -triazene, respectively, from p-xenylamine and m-xenylamine whose mineral acid salts are insoluble in water, it is so economical and expeditious that it may advantageously be employed to make, 1,3-bis (o-xenyl) -triazene from o-xenylamine even though the mineral acid salts of this amine are soluble in water.

The process of my invention may be used to prepare the triazenes of primary aromatic amines generally whose mineral acid salts are either sparingly soluble in water or readily hydrolyzed by water such as the following: ZA-dinitroaniline, i-chloro-2-methylaniline, 2,4-dichloroaniline, 2- nitrol-methylaniline, 3-nitro-2,4,6-trimethylaniline, 3,4-dichloroani1ine, 2,4,6-trichloroaniline, 2,6-dibromoaniline, meta-amino diphenyl, 4'- chloroi-aminodiphenyl, 4' nitro 4 aminodiphenyl. The primary aromatic amines employed are soluble in the solvents enumerated above which greatly facilitates the reaction since the alkyl nitrite employed is very soluble in the solvents named. The continuous removal of the triazene as it is formed from the reaction centers by precipitation due to its insolubility in the solvent also greatly expedites the reaction.

As the solvent used as the reaction medium, I may employ any normally liquid mono-cyclic aromatic hydrocarbon which includes benzene and its alkylated homologs, as well as any mononuclearly-halogenated derivative of benzene or an alkylated homolog thereof. Specific examples of solvents falling within this classification are benzene, toluene, o-xylene, m-xylene, p-xylene, ethyl benzene, any of the trimethyl benzenes, n-propyl benzene, isopropyl benzene, cymene, any of the diethyl benzenes, etc., fluorobenzene, fluorotoluenes, fluoroxylenes, chlorobenzene, chlorotoluenes, chloroxylenes, bromobenzene, bromotoluenes, bromoxylenes, iodobenzene, iodotoluene, iodoxylenes, etc. The solvent used will generally have a bci ing point of between and 200 C.

Any alhyl nitrite may be used in the practice oi m invention, examples being methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, n-amyl, isoamyl, n-hexyl, n-heptyl, n-octyl, etc. Generally the alkyl nitrite will be one having from one to five carbon atoms in the alkyl'group. I prefer to use an alkyl nitrite Whose corresponding alcohol boils sufiiciently above or below the solvent used that a mixture of the alcohol and the solvent, which is present in the mother liquor from which the precipitated xenyltriazene has been separated, can be "readily resolved by ordinary fractional wdistillation into separate fractions of alcohol an'd'solvent which can be reused in the process, the solvent fraction being recycled for use in a subsequent reaction and the alcohol fraction beinglempl'oyedtoge'nerate more alkyl nitrite which is utilized in a subsequent reaction.

Preferably the boiling points of the solvent and the alcohol corresponding to'the alkyl nitrite are at least 10 C. apart, so as to permit separation by ordinary fractional distillation I have'discovered'thatmethyl nitrite canbe especially advantageously employed as the alkyl nitrite in the;.process of my. invention. I have found that methyl nitrite readily condenses with the xenylamines when they are dissolved in solvents. such as benzene, toluene, xylene, o-r chlorobenzene, or the like from the class given above to give symmetrical xenyltriaz enes. Methyl nitrite haS mQ Iny dvantages over the higher alkyl nitrites which have been commonly used heretofore such as amyl nitrites, and so far-as I am aware, methyl nitrite has never been usedin the preparation of a triazene. Methyl nitrite offers the advantage ,thatit can be generated simultaneously with its use in the reaction which ofiers ad anta sgov r hep el m n r preparation o the higher alkyl nitrites previously used. Methyl n r te... may, conv niently. b generated y the interaction of an alkali metal nitrite suchas sod um nitrite, with rncthyl alcohol and sulfuric acid-:1 .I nr f bt n rate i in 's e q o esca ate i tberea ie zon a d erm h m thy it tam on fr mih ssn a erz di ectlyciniqith ea t- Met l it a t e esi eu see b in a se b i sre 12 Q. so that it ca n be generated readily withgu ating... There is no need forisolation or 2 et e qilt me hyin r te s n it is in eubsheiie lmure erm s ts se eda 99 sensa ion .ei'j ie. m zrl'i r in uchlas amyl iitrit'e. 'The use of methyl nitrite ore 'econ'omical sin'cesmaller duantitiesof alcohol'need beiised because. of thelow molecular weight of maths/ amon Th 'pro'duct prepared fronijamyl nitrite 'smjells'str'o'ngly of objectionable va lefe acid dua to traces of amyl alcohol which we -n t removed and which on"drying oxidized to valeric acid. Methyl nitrite does not leave cont'amina tion of i the ,product because of the volatilitybfany methyl: alcohol present in the product [Ifhe met yl 'alcohol'formed in the reaction can be readily recovered by fractional "disunauqn'orthe' mother liquors since the difference between the 'boiling'"point of methyl alcohol and such 'solve'r'its as xyleneand toluene is much greater thanbetwe'en' am'yl' alcohol and the same solvents. The simultaneous formation and use of methyl 'nitritesaves a great deal of time. The excess of methyl nitrite'is more readily removed than is an excess of a higher boiling alkyl nitrite. I have found that when methyl nitrite is used there is no induction period as is the case with the amyl nitrites. The induction period when amyl nitrites are employed is undesirable especiall when large batches are made because the reaction becomes violent when it once starts.

The reactions involved-in the formation of the methyl nitrite may be indicated as follows:

tain high yieldsof the Xenyltriazenes when using methylnitrite, it is necessary to employ a considerable excess thereof over the amount theoretical-ly required by the reaction, which in'the case of the preparation of 1, 3 -bis(p-xenyl) -triazene; may be indicated by the following equations:

r. ranges from 0.75;1 to 1.25:1. If only the theoretical quantity' 'of jmethyl" nitrite is used with p-Xenylam'ine the'y'ieldfal'ls from 84 per cent to 3 2iper'ce'nt and thaprdirctinelts at C.'whi ch indicates that considerfable impurities are present. All; yields "referred"to"her'ein are based on the kenylam'ine' used. I

In the ease of the' other alkyl 'nit'rit'es, I generallyernploy only about the theoretical amount or thenitriteinainely'that amount required to give a molar ratio of alkyl'nitri'teto amine of 0.531. EX- cesses' over theoretical may be "employed although use thereof offers no advantage.

'The' amount 'of solvent employed as the reaction medium in carrying out the present invention may varywidely. Theamount th'ereof' should *th'atfthe resulting reaction 'mixture is pumpable'despitethe'presence therein of the precipitated xenyltriaz'ene. Use of'siich an amount greatly-facilitates subsequent recovery operations, 'parncnany the' step of separating the A precipitated product which is usually-done by filtration. A greater 3 amount of -'s'(")l-\"/ent"'than this may be used but it s16ws up thereaction and increases the *costsf- "particu'l'arly of-handling and solvent recovery, 'andthe efore' is not desirable. l Those skilled-in the 'artwill'be readilyenabled to se'lect a "proper amount" of solvent in the light-bf this disclosure. Ordina'ri1y-'the weight Of SO'IV 'eDt WiH range between 1.0 and 4 times theweight of the Xenylamine.

The reaction may be carried out under any suitable reaction conditions which promote the desired formation of the xenyltriazene by condensation of the alkyl nitrite and the xenylamine. Ordinarily the temperature of reaction will range from to C. If necessary the reaction mixture may be cooled during the reaction in order to keep the temperature from rising unduly. The time of reaction cannot be specified exactly since it will vary widely depending on conditions but it preferably is sulficient to permit the reaction to proceed to substantial completion. Ordinarily the reaction mixture is allowed simply to stand until precipitation of the xenyltriazene is substantially complete. If desired the reaction mixture may be stirred during the addition of the alkyl nitrite and it may also be stirred during the subsequent period of time to break up the precipitate.

The process of my invention is ordinarily conducted in a batchwise manner but it may be carried out continuously by appropriate modification in a manner obvious to those skilled in the art.

Following are specific examples of the practice of my invention:

Example I To a solution of 200 g. of p-xenylamine in 800 cc. of benzene there was added 84 cc. of isoamyl nitrite, keeping the reaction mixture at room temperature, and the mixture allowed to stand at this temperature with cooling if necessary, depositing crystals of 1,3-bis(p-xenyl) -triazene over a period of twenty-four hours. The solid was then filtered off and after washing with benzene and air drying, melted at 140-141" C. with gassing. Yields as high as 95% of the theoretical were obtained. The benzene and isoamyl alcohol were separately recovered by fractionation of the mother liquors and re-used in subsequent runs.

Example II Example III To a one litre three-necked fiask equipped with a dropping funnel, a sealed stirrer and a water cooled condenser, there was added 32 g. (0.46 moles) sodium nitrite, 20 cc. (0.50 moles) methanol and 20 cc. of water. The water-cooled condenser was connected to the inlet tube of another reactor which consisted of another one litre three-necked fiask equipped with the above mentioned inlet-tube, a sealed stirrer, a water cooled condenser and a thermometer. Into the second reactor there was placed a solution of g. (0.41 moles) of o-xenylamine in 300 cc. of toluene. Both stirrers were started, and into the first reactor there was dropped over a period of forty-five minutes, 51 cc. of sulfuric acid solution made up from two volumes of water and one volume of sulfuric acid. The generated methyl nitrite gas bubbled through the o-xenylamine solution.

The temperature rose from room temperature to 30 C. over the addition period. After stirring a few minutes, subsequent to the addition period, until methyl nitrite ceased formation, the clear reaction solution was allowed to stand. After several hours when a precipitate of the triazene 6 began to form, the stirring was renewed to keep the mixture broken up. The precipitation was complete in 12-24 hours. The first crop of 1,3- bis(o-xenyl)-triazene was then filtered off and washed with toluene. The filtrate was concentrated under partial vacuum to about cc., recovering methanol and toluene. A second crop of the triazene was obtained from the concentrate on cooling. Total yield was 65.7 g or 89% of the theoretical. The composite product melted at 159-160. The methanol and toluene were recovered by fractionation.

Example IV Into a solution of 70.6 g. of p-xenylamine in 150 cc. of toluene there was passed a stream of methyl nitrite generated by dropping a solution of 51 cc. of.2:1 water-95% sulfuric acid into a mixture of 32 g. sodium nitrite, 20 cc. methanol and 20 cc. water, the temperature rising to 25 C. When all the triazene had precipitated it was filtered ofi and dried. The yield of 1,3-bis(p-xenyl) -triazene was 83.6% of theory, the product melting at The methanol and toluene were recovered from the mother liquors by fractionation.

Example V To a solution of 500 g. of p-Xenylamine in 1500 cc. of benzene there was added 154 g. of n-butyl nitrite and the mixture was allowed to stand at room temperature until precipitation was complete. The yield of 1,3-bis(p-xenyl) -triazene that was filtered off and dried was 65% M. P. 135.

I believe that I am the first to prepare 1,3- bis(o-xenyl)-triazene which has the structural formula 3N=DPNHC O C) and which is claimed as a new chemical compound in my copending application Serial No. 780,746, filed of even date herewith, now Patent No. 2,448,155.

The symmetrical xenyltriazenes made in accordance with my invention have many uses. They may be employed as chemical intermediates for the synthesis of other chemicals, especially dyestuffs. They are very useful as blowing agents for the manufacture of expanded rubber and plastics, which is covered in the copending application, Serial No. 780,744, filed of even date herewith, now Patent No. 2,448,154 in the name of the present applicant and another.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The process of preparing symmetrical xenyltriazenes which comprises reacting a xenylamine with an alkyl nitrite, said xenylamine being in solution in a normall liquid solvent selected from the group consisting of benzene, homologs of benzene, mono-ring-halogenated benzene and monoring-halogenated homologs of benzene, effecting precipitation of the xenyltriazene, and separating the precipitated xenyltriazene from the resulting reaction mixture.

2. The process of preparing symmetrical xenyltriazenes which comprises reacting a xenylamine with an alkyl nitrite, said xenylamine being in solution in a normall liquid solvent selected from the group consisting of benzene, homologs of ben zene, mono-ring-halogenated benzene and monoring-halogenated homologs of benzene, maintaining a reaction temperature of from 20 to 60 C against effecting preoipitationof the 'xen'y ltriazene, and separating the "precipitated xenyltri'azene from the resulting reaction mixture.

3. The process of preparing'symmetrical Xenyltriazenes which comprises reacting axenyl-a-mine with methyl nitrite, said xenyla-mine"being in soluti'on in a normally liquid solvent selected f-rom the groupconsistingo'f benzene, homologs-o f b'enzene, mono-ring-halogenated ib'enzene and'rnonering ha'logenated homologs "of benzene, effecting precipitation of the xeny ltriazene, and separating the precipitated xenyltriazene-from-the resulting reaction mixture.

4. The process of preparing symmetrical xenyl- 'triazenes which comprises passing methyl nit-rite into a solution of a Xenylamine in a normally liquid solvent selected from the group consisting of benzene, homologs of benzene, mono-ringhalo'genated benzene and mono-ring-h2ilogenated homologs of benzene in a reaction -zone, e'ffecting precipitation of the Xeny'ltriazenein said reaction zone, and separating the precipitated xenyltriazene from the resulting reaction mixture.

'5. The process of claim 3 wherein said methyl nitrite is employed in an amount such that the molar ratio of methyl nitrite to said Xenylamine ranges from 0.7521 to 1.25:1.

6. The process of preparing 1,3- bis('o-xeny1)- triazene having the structural formula which comprises reacting o-xenylamine with 7 which comprises reacting p-xenylamine with methyl nitrite, said p-Xenylamine being in solution in a normally liquid solvent selected from the group consistingof benzene, homologs of benzene, inono-ring-halogenated benzene and mono-ringhalogenated homologs of benzene, efiecting precipitation of the 1,2-bis(p-xenyil)-triazene, and separating the precipitated 1,3-bis(pxenyl)-tria-zene .from the resulting reaction mixture.

8. The process of making symmetrical xenyltriazenes which comprises passing methyl nitrite into a solution of a xenylamine in a normally liquid solvent selected from the group consisting of benzene, homologs of benzene, mono-r'ing-hal- S 'ogena'ted benzene and mono-rlng-halogenated *h'omologsof benzene in a reaction zone.

'9. The qaro'cessdfmaking symmetrical aryl triazenes from primary aromatic amines capable of form'ing symmetrical 'aryl triazenes and selected from the-group consisting of those primary aromatic amines whose mineral 'acid salts are insoluble in water and those primary aromatic amines whose'minera'l acid salts are readily hydrolyzedmy waterand consequently difficultly diazotizablewhic-hcomprises dissolving the primary aromatic amine in .a normally liquid solvent selected from the groupconsisting-of benzene, homo'logs of benzene, *mono-ring-halogenated benzene and mono-ring-halogenated 'homologs of b'enzene and-adding an'alkyl nitrite.

10. 'Theprocess of making symmetrical aryl triazenes from primary aromatic amines capable of forming symmetrical aryl triazenes and selected from "the group consisting of those primary aromatic amines whose mineral acid salts are insoluble in water and those primary aromatic amines whose mineral acid salts are readily hydrolyzed by water and consequently di'fiicultly diazotizable which comprises dissolving the primary aromatic amine in a normally liquid solvent selected from the group consisting of benzene, homologs of benzene, mono-ring-halogenated benzene and mono-ring-halogenated homologs of benzene, and passing vmethylnitrite into theselution. of said .amine .in .a reaction zone.

, '11. "The process of making symmetrical xen-yltr'iazenes which comprises reacting a xenylamine in solution in .a :normally liquid solvent selected from the group consisting of benzene, .homologs of benzene, .monoaringahalogenated benzene and mono-ring-halogenated homologs of benzenewith anialkyl nitrite.

.HENRY I-I. RICHMOND. REFERENCES CITED The following references are of record in the file of this patent:

FLEREIGN PATENTS Number Country Date 727,293 'France Mar. 21, 1932 575,832 Germany May 3, '1933 OTHER REFERENCES vol. 8, page 1074 vol. 583, page 1914, 

6. THE PROCESS OF PREPARING 1,3-BIS(OXENYL)TRIAZENE HAVING THE STRUCTURAL FORMULA 